John Harris (The Guardian, 8 June) is no doubt right to say that the left is feeling frustrated and dispirited. But does that mean that we are bereft of ideas? I think not.

The frustration is born, I think, of the fact that ideas that seem so obvious and rational appear to have so little traction. The challenge for us, in other words, is not so much to come up with brilliant new insights, as to find ways of being better understood and commanding greater support.

On the face of it, the task should be an easy one. When events have conspired to demonstrate just how far the country has veered off course, there has never been a better time to argue that a change of direction is needed.

The unregulated market is self-correcting and infallible? Business leaders have all the answers? Government should step aside and allow business to get on with it?

None of this, surely, is credible in light of the disaster created by the greed, incompetence and irresponsibility of private sector operators and the intervention required of government that alone allowed us narrowly to avert full-scale depression.

Yet, these lessons have not been learned. The problems created by the wealthy, it seems, have to be shouldered by the poor and the unemployed. The rich need to be placated in the hope that their wealth, in an increasingly unequal society, will somehow “trickle down”. The economic power of government must be sidelined in the hope that contraction will, with the help of the confidence fairy’s ministrations, lead miraculously to recovery.

It is not that we are left at a loss, confounded by the superior expertise and arguments of our opponents. We do not need to cast around and dig deep for new ideas when there is no shortage of convincing and commonsense responses to these continued mistakes.

Markets – valuable servants but dangerous masters – function best when they are properly regulated. The greatest threat to our financial viability is that we fall deeper into recession. Government spending is essential in recession, both to protect the vulnerable and to stimulate recovery. Full employment is the most important goal of economic policy and the most valuable stepping stone to a full recovery. To widen inequality and to drive people further into poverty is to threaten the very fabric of our society.

There are powerful and widely endorsed arguments to support each of these propositions. The left should not, in other words, beat itself up for its supposed failure to come up with appropriate solutions to our problems. It should ask itself instead why a rival and implausible narrative has achieved wide acceptance, and why the obvious commonsense responses fail to carry conviction.

It is at this point that the real difficulty arises. The left, at least in the form of the Labour Party, has consistently undermined its own position by demonstrating in government that it prefers the case made by its opponents to its own. Indeed, New Labour – at a time when the Tories themselves had had enough of the Thatcherite revolution – insisted on regarding themselves as heirs to the Thatcherite legacy, and persuaded themselves that embracing it was the essential pre-condition for election victory.

So, both the Blair and Brown governments expressed confidence in unregulated markets and financial markets in particular. They looked to the private sector – in areas like health and education – as a preferable alternative to public provision. They uncritically supported the City as the flagship of prosperity for all. They were relaxed about widening inequality – and “intensely relaxed” about people becoming “filthy rich.” They presided over high levels of unemployment.

All this, we were told, in the interests of contesting for the “centre ground”. But the centre ground is a slippery concept. It is to be found where you choose to find it or where you allow it to be. It can – and did – move sharply to the right, when ground that was previously to its left was abandoned, and right-wing opponents took advantage of that surrender to keep moving right.

The left is at present damagingly incapacitated by its demonstrable failure, when it really mattered – in government – to show any confidence in left prescriptions. They found themselves, in pursuit of an ill-defined centre ground, constantly chasing it as it disappeared rightwards.

Politics in a democracy is largely a matter of who controls the agenda. The right begin with the huge advantage of overwhelming media support from right-wing media barons. They do not need additional help from acquiescent opponents.

There is little wrong, I believe, with much of the left analysis of the country’s current plight, particularly when that analysis is so strongly supported by experience. The deficiency lies in the confidence with which that analysis is advanced. We must draw a line under our recent unhappy experience and, with the force, eloquence and conviction of our arguments, define for ourselves the centre ground rather than let others do it for us.